Harris, who missed time because of a left oblique strain, will be a backup outfielder. Before getting hurt, Harris saw a lot of time at second base and was 2-for-9 in five games.
With Harris back, the Nationals sent Justin Maxwell to Triple-A Syracuse to play every day and get more at-bats.
Maxwell was 3-for-8 in six games and brought a lot of energy to the club because of his speed and hard work. He started Sunday against the Mets and went 2-for-5 in an 8-1 victory.
As for Guzman, he will return to action after missing time because of a left hamstring strain. He will be the new leadoff hitter, while second baseman Anderson Hernandez will move down to the No. 8 slot.
Guzman was 17-for-33 (.515) before getting hurt against the Phillies on April 13.
"I expect him to continue to hit the way he has been hitting the last couple of years," manager Manny Acta said. "Even though he doesn't walk as much, he is making up [for the high on-base percentage] by flat-out hitting."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.